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I'm using sendmail on a dedicated server I lease from APlus.net, running FC4. This server has two domain names, including the original generated by APlus.net incorporating its static IP address (216-55-142-104.dedicated.abac.net) and the domain name I registered for it . If you reverse IP lookup the IP address, you only get the APlus.net name, not mine. I've had trouble choosing a domain name for confDOMAIN_NAME that doesn't cause lots of email to be rejected as SPAM, because I think receiving SMTP servers both (a) do a reverse IP address lookup on the address which connected to them and discover the name doesn't match the name given by the EHLO/HELO command, and (b) check the EHLO/HELO name for various suspicious characteristics. I'm assuming the confDOMAIN_NAME setting is used as the EHLO/HELO domain name. If I use the APlus.net name for the server in confDOMAIN_NAME, various SPAM filters give all the email really high scores because of the IP address incorporated in the name. If I use my domain name, other servers flag me as SPAM because the reverse IP address lookup gives the APlus.net name.
I'm a sendmail newbie. Am I understanding the problem correctly? Any advice?
The best way to solve that is to write to your ISP for the server (I'm guessing aplus.net, but the reverse says abac.net). Tell them you want to run a mail server, and you need a PTR (reverse DNS record) for the server. If the forward DNS name of your server is mail.jackandjill.com, then the PTR should be the same, mail.jackandjill.com, coupled with the IP address.